This is more of a question for my benefit (history essay) than one to inform others, so sorry about that. I've been searching on google to no avail.
My history professor mentioned a tragedian who put on a play depicting a recent battle (perhaps in the Peloponsian war) that made the audience so sad that he was punished in some way. At another time, a comedy was written about the same event but it made people laugh so much that the comedian wasn't punished. Is anyone familiar with the tragedian or either of the plays?
The play you're looking for is [Phrynichos'](http://en.wikipedia.org/wiki/Phrynichus_(tragic_poet)) Sack of Miletos. Miletos fell in 494; the play may possibly have been staged in Athens in 492, when Themistokles was archon (Themistokles in later decades showed himself to be a fan of Phrynichos), though there's no guarantee of that.
Herodotos 6.21 reports the following story about the play:
[the Sybarites and the Athenians] made it clear that they were excessively pained by the sack of Miletos: and in particular, when Phrynichos wrote a play on the sack of Miletos and staged it, the theatre fell into weeping, and they fined him 1000 drachmas for reminding them of their own misfortunes, and ordered that no one should stage this play.
The bit about ordering that no one stage the play probably refers to follow-up performances in the rural demes of Attica. On the face of it the story doesn't look too unlikely, but we've got no corroboration, so don't put too much stock in it.
All of Phrynichos' works are lost, but we have reports that his work was extremely influential on Aischylos and Euripides. He was active from the 520s until at least the early 470s; he was also known for a play on the battle of Salamis, called the Phoenician Women (which influenced Aischylos' Persian Women, on a similar theme).
Your mention of a comedy on the sack of Miletos: I hadn't heard that before. It could be true, but I wonder if it might be a misreporting or misunderstanding of some kind. The history of lost Greek dramas is a pretty specialised field, so I wouldn't count on someone showing up to reveal all -- the most secure way to find out more would be to learn ancient Greek and Latin, and go ploughing through all eight volumes of Poetae comici graeci to try and locate a reference... of course if no such reference actually exists, that could be a bit of a waste of time.
(PS. Don't put too much stock in the Wikipedia page on Phrynichos; it has a couple of errors. Go look at the New Pauly or the Oxford Classical Dictionary instead.)